Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quantos rankings têm uma média de rebotes menor que 6.1?
 ###Tabelas: CREATE TABLE marriage_statistics (marriage_statistics_id AUTO_INCREMENT PRIMARY KEY, Year VARCHAR, Marriages between men INT, Marriages between women INT, Same-sex marriages INT, Total marriages INT, % same-sex marriages VARCHAR) CREATE TABLE public_companies (public_companies_id AUTO_INCREMENT PRIMARY KEY, State Rank by Revenue INT, Company Name VARCHAR, National Rank INT, Revenue ($billions) 2012 estimate VARCHAR, Headquarters City VARCHAR, Known for VARCHAR) CREATE TABLE rebounds (rebounds_id AUTO_INCREMENT PRIMARY KEY, Rank INT, Player VARCHAR, Years VARCHAR, Games INT, Reb. Avg. INT, Total Rebounds INT) CREATE TABLE ratings (ratings_id AUTO_INCREMENT PRIMARY KEY, Season VARCHAR, Episodes INT, First airdate VARCHAR, Last airdate VARCHAR, Nielsen ranking VARCHAR) CREATE TABLE title_history (title_history_id AUTO_INCREMENT PRIMARY KEY, Reign INT, Days held VARCHAR, Location VARCHAR, Successful defenses INT, Event VARCHAR)  
SELECT COUNT Rank FROM rebounds WHERE Reb. Avg. < 6.1